The present invention relates to a valve operating mechanism for a poppet valve of an internal combustion engine, said mechanism comprising a spring retainer made of light alloy such as Al alloy which is mounted to the poppet valve via steel cotters, thereby increasing load of falling the cotters out of the lower end of the spring retainer.
FIG. 6 illustrates an example of a known valve operating mechanism of an internal combustion engine, in which an A1 alloy valve spring retainer 23 which has a taper bore 22 and a spring-retaining flange 23a is engaged with the upper end of a poppet valve 21 via a pair of steel cotters 24. An annular bead 24a of each of the cotters 24 is engaged in an annular groove 21a of the poppet valve 22 so that the valve spring retainer 23 may not come out upwards.
Between the lower surface of the spring-retaining flange 23a and a cylinder head (not shown), a valve spring 25 is provided, and the poppet valve 21 is always urged upwards by the valve spring retainer 23.
The numeral 26 denotes a rocker arm which is engageable on the upper end of the poppet valve 21, and is moved up and down by a rotary cam (not shown) to open and close the poppet valve 21. In the valve operating mechanism, the cotters 22 and the valve spring retainer 23 are integrally secured to the poppet valve 21 by wedge-like engagement of the cotters 24 with the bore 22. To increase securing force, taper angle of the bore is decreased, and roughness of contact surface between the bore 22 and the cotters 24 is decreased to decrease frictional resistance, thereby strengthening wedge-like engagement.
However, in a valve operating mechanism which has a relatively low mechanical strength Al alloy valve spring retainer 23, when the bore 22 is plastically deformed and expanded owing to increase in wedge-like engagement, the cotters 24 fall gradually owing to low frictional resistance of the contact surface between the bore 22 and the cotters 24. The valve spring retainer 23 moves up gradually, so that load to the valve spring 25 is decreased to decrease the maximum rotation number of surging, so that engine performance is deteriorated.
When the cotters 24 fall deeply, the lower end of the valve spring retainer 23 is liable to cause cracking and to be damaged,. so that the cotters 24 come out. To solve the problem, the valve spring retainer 23 or the lower portion thereof increases in external diameter to increase rigidity and load of the cotters 24.
However, the valve spring retainer 23 becomes larger to increase its weight. For Al alloy valve spring retainer made to lighten its weight, it will not be advantageous.
In view of the disadvantages as above, it is an object of the present invention to provide a valve operating mechanism for a poppet valve of an internal combustion engine to prevent a pair of cotters from falling out of a bore of a valve spring retainer.